Reovirus infected L-cells are being used to study the specificity of immunological reagents in precipitating polyribosomes synthesizing specific proteins. Reovirus contains 6 polypeptide species; and 10 species of double stranded RNA. The virus directs the synthesis of 10 species of messenger RNA. These mRNA's can be obtained from the polyribosomes of infected cells, and will hybridize specifically with denatured viral double stranded RNA. We have made antibodies to viral proteins and are attempting to immunoprecipitate the polyribosome synthesizing these proteins to answer the following questions: 1. Which mRNA codes for each of the proteins within the virion? 2. Do immunoprecipitated polyribosomes contain mRNA's other than those specifying the protein toward which the antibodies are directed?